On Gases under the Influence of the Electric Discharge, 357 

 for the stream-line f ds, 



It does not seem to me to be possible in this general case to 

 determine the forms of the stream-lines, or the resistance 

 which the friction of*the fluid opposes to the motiort^of the 

 sphere. In the case where the motion is symmetrical to the 

 axis of x, the resistance has been determined by Lamb Q Trea- 

 tise on the Motion of Fluids/ page 126) by means of the dis- 

 sipation-function ; that process would scarcely be applicable 

 to such a complicated case as the one in hand. I do not see 

 that any other results of importance can be obtained from 

 further study of this problem, unless, indeed, the velocities 

 u, v, w can be given in some other form than that of an infinite 

 series. 



Washington, June 12, 1880. 



XLII. On the Thermic and Optical Behaviour of Gases under 

 the Influence of the Electric Discharge. By E.Wiedemann*. 

 [Plate IX.] 

 1. Introduction. 



IN two previous experimental investigations (Wied. Ann. v. 

 p. 500, 1878, vi. p. 298, 1879) I have examined the lumi- 

 nosity of gases under the influence of the electric discharge. 

 The result of the first investigation was, that when a mixture 

 of two gases is exposed to the electric discharge, of which the 

 one is a metallic vapour and the other nitrogen or hydrogen, 

 the lines of the metallic vapour are seen in the spectrum, 

 while those of the other gas remain invisible ; so that the 

 propagation of the electricity is due entirely to the metallic 

 vapour. The discharge in it is entirely discontinuous. The 

 same result has been recently obtained by H. W. Vogelf, by 

 photographic methods. 



The second investigation showed that the temperature of 

 the gas illuminating a Geissler's tube may be below 100°. 



This last result has been recently confirmed by HasselbergJ. 

 Hittorf also has shown, but without accurate measurements, 

 that the same conclusion is throughout in agreement with 

 the phenomena. 



* Translated from "Wiedemann's Amiakn, No. 6, 1880, with additions 

 and corrections by the Author. 



+ H. W. Vogel, Beibl. iv. p. 125, 1880. 

 X Hasselberg, Beibl. iv. p. 132, 1880. 



